Document FR2969967 discloses an example of such a rail, where the lock is integral to the free end of the spring blade and moves vertically with this free end upon actuation of the control member.
Rails of this type are of particularly simple and robust construction; they are also particularly compact, as the spring blade and lock are located within the inside space of the rail. However, they have the disadvantage of imposing a particular type of lock with specific unlocking kinematics.